1. Field of the Invention
The invention relates to implantable cardiac devices in general and to implantable heart stimulators such as cardiac pacemakers, implantable cardioverter/defibrillators (ICDs) or a combination thereof in particular.
2. Description of the Related Art
Heart stimulators such as implantable pacemakers can be used for treating a plurality of different malfunctions of a heart. Many pacemakers are designed to treat the right chambers of a heart, the right atrium and the right ventricle, only.
In such case, also the delay between a right atrial contraction and a right ventricular contraction needs to be optimized in order to properly synchronize right and left ventricular contraction and the right atrial contraction. The delay interval between a right atrial contraction and the right ventricular contraction usually is called atrioventricular delay interval that is abbreviated AVD.
Biventricular pacemakers are able to pace both ventricles of a heart.
Biventricular pacemakers are used for a cardiac re-synchronization therapy that shall synchronize right ventricular contraction and left ventricular contraction to improve the output of a heart exhibiting a cardiovascular disease. In particular, cardiac synchronization therapy is used to treat heart failure in patients with wide QRS complex that results from a delayed excitation of the left heart side. It is believed, that a main contributor to heart failure (the heart's inability to generate enough cardiac output) is an asynchronous mechanical contraction of the left and right side of the heart.
In order to restore an optimum cardiac output by proper synchronization of consecutive contractions of the chambers of a heart, the duration of a delay interval between a right ventricular contraction and a left ventricular contraction also needs to be optimized. This delay interval is called interventricular delay or interventricular delay interval or interventricular interval and often times is abbreviated VVD.
Furthermore, in order to restore an optimal cardiac output the proper sequence of the contractions of the chambers of a heart needs to be optimized. Positive values of the VVD denote that the rightventricular chamber is stimulated first and after the VVD the leftventricular. Negative values of the VVD denote that the leftventricular chamber is stimulated first, followed by the right ventricular chamber after the VVD.
US 2005/0131469 discloses a hemodynamic optimization system that automatically adjusts atrioventricular delay and the interventricular delay until maximum hemodynamic output is achieved. According to US 2005/0131469 hemodynamic information can be gathered via impedance measures, QT-interval, accelerometer, mixed venous oxygen duration, cardiac output or similar marker, intracardiac pressure monitoring, blood pressure, temperature and other suitable physiologic parameters. According to U.S. Pat. No. 4,303,075 the atrial ventricular delay is optimized until stroke volume reaches a maximum. Stroke volume is measured by way of an impedance processor for determining a peak to peak amplitude that corresponds to the stroke volume of the heart.
Depending on the mode of operation of the heart stimulator, triggering and delivery of stimulation pulses is inhibited if a natural contraction of a respective heart chamber is sensed prior to expiration of a respective delay interval. Thus, stimulation pulses are only triggered if needed. Such mode of operation is called demand mode.
Another aspect of state of the art heart stimulators is called demand pacing. In a demand pacing mode a stimulation pulse only is delivered when no natural (intrinsic) contraction of a respective heart chamber occurs during a preset interval. Stimulation of a heart chamber causing a so called paced event is inhibited if a natural contraction of that heart chamber, called sense event, is sensed prior to expiration of a respective interval, e.g. AVD or VVD. A contraction of a heart chamber, either stimulated (pace event) or intrinsic (sense event), is called event. Stimulation of a heart chamber is also called pacing a heart chamber.
In such demand mode, a heart stimulator puts out an electrical stimulation pulse to a heart chamber at time out of a respective delay interval unless a sense event occurs prior to expiration of a respective delay interval. In particular, a stimulation pulse to the right ventricle is triggered and delivered at the end of the atrioventricular delay interval if no natural right ventricular contraction is sensed prior to expiration of the atrioventricular delay interval. Similarly, a stimulation pulse to the left ventricle is triggered and delivered if no left ventricular contraction is sensed prior to expiration of the interventricular delay interval.
In order to be able to operate in a demand mode, a heart stimulator comprises sensing stages for sensing natural (also called intrinsic) contractions of a respective heart chamber. A natural contraction of a heart chamber is also called an intrinsic event (or “sensed event” since it only becomes relevant if such intrinsic event is actually sensed) in contrast to a contraction of a heart chamber due to stimulation that is called a paced event. For each heart chamber to be stimulated, e.g. right atrium, right ventricle and left ventricle, a separate sensing channel (including sensing stages) is provided in order to discriminate between intrinsic events of different origin. Atrial events are usually designated with A and ventricular events are designated with V since the atrioventricular delay is the delay between an atrial event and a ventricular event it is abbreviated AVD.
Another parameter to be controlled by a heart stimulator is the heart rate. Usually, a base rate is set that determines a minimum heart rate that is enforced by the heart stimulator if the base rate is not met or exceeded by the natural, intrinsic heart rate of the heart.
Setting of the base (or basic) rate may differ between day and night in order to meet the natural circadian variations in a heart cycle.
Most current implant devices allow programming of the night basic rate. The start and end time of the night phase can be empirically set through programming the implant device. On the other hand, different methods have been proposed to allow the implant device to automatically detect the day and night phases, for example, by analyzing the signals measured by activity sensor (U.S. Pat. No. 5,300,092 and U.S. Pat. No. 5,350,408), by analyzing the activity variance provided by the activity sensor (U.S. Pat. No. 5,476,483, and U.S. Pat. No. 6,128,534), by analyzing both activity sensor signal and the cardiac rhythm information (U.S. Pat. No. 5,645,576), by analyzing the QT intervals (U.S. Pat. No. 5,861,011), by analyzing the blood temperature (U.S. Pat. No. 5,814,087), or by analyzing the impedance-based respiration signals (U.S. Pat. No. 6,519,494 and U.S. Pat. No. 6,773,404). In addition, the method for day-night transition of pacing rate was also disclosed (U.S. Pat. No. 5,733,312).
The following lists the most relevant patents found and considered by the inventors:
Pat/Appl. No.Issued DateInventorsAssigneeU.S. Pat. No. 5,300,092April, 1994SchaldachBiotronikU.S. Pat. No. 5,350,408September, 1994SchaldachBiotronikU.S. Pat. No. 5,476,483December, 1995Bornzin et al.PacesetterU.S. Pat. No. 5,645,576July, 1997Limousin et al.ELAU.S. Pat. No. 5,733,312March, 1998Schloss et al.PacesetterU.S. Pat. No. 5,814,087September, 1998RenirieMedtronicU.S. Pat. No. 5,861,011January, 1999StoopVitatronU.S. Pat. No. 6,128,534October, 2000Park et al.PacesetterU.S. Pat. No. 6,519,494February, 2003HuttenBiotronikU.S. Pat. No. 6,773,404August, 2004Poezevera et al.ELA
Yet another commonly known aspect of modern heart stimulators concerns an aspect called hysteresis. Hysteresis is applied to promote intrinsic contractions of a heart chamber, e.g. the right ventricle by prolonging an AVD by a hysteresis interval after a natural contraction of said heart chamber was sensed thus increasing the likelihood that another natural contraction of said heart chamber falls into the prolonged AVD. Only if no intrinsic contraction of the heart chamber is sensed during the prolonged AVD, the heart stimulator switches back to the regular (non hysteresis) AVD.
Besides the heart rate, other cardiac electrophysiological properties also show certain circadian patterns.
The AV node is innervated by both sympathetic and vagal fibers. The AV nodal conduction time is shortened as sympathetic tone increases, or lengthened as vagal tone increases. It is well known that a person's vagal tone is enhanced during sleep, resulting in prolonged AV conduction time at night.
On the other hand, for three-chamber cardiac resynchronization therapy (CRT) devices that deliver bi-ventricular paces to synchronize the left and right ventricular contractions, the VV delay must be optimized. It is known that the optimal VV delay has substantial inter-subject variability. In addition, for each individual patient, the optimal VV delay also varies based on the heart rate or activity level. Therefore, the circadian variation of the optimal VV delay is also expected.
Therefore, there is a need for the implant device can automatically adjust the device AV delay and VV delay for day and night, respectively.
Yet another limitation common to all existing implant devices is that the device measures and maintains daily (day and night) lumped statistics, thus cannot reveal the potential circadian pattern of cardiac electrophysiological behaviors. Therefore, there is a need for the implant device to measure and maintain the device statistics for day and night independently, thus potentially yielding more diagnostic information.
For the purpose of this disclosure, the following abbreviations are used are used:
AbbreviationMeaningACCAutomatic Capture ControlAp, APAtrial pace (stimulation) eventArsrefractory atrial sense eventAs, ASAtrial sense eventAAny atrial eventAESAtrial extra systoleAFAtrial fibrillationATAtrial tachycardiaATPAnti tachycardia pacingATTAutomatic threshold trackingAVatrioventricularAVDAV delay as applied by the pacemaker(in contrast to intrinsic AV delay)ΔAVDOffset AVDCRTcardiac resynchronization therapyDIntra cycle delay interval (AVD or VVD)ΔDOffset intervalLVpLeft ventricular stimulation pulsePMTPacemaker mediated tachycardiaPVARPPost-ventricular atrial refractory periodRARight atrial eventRVRight ventricular eventRVpRight ventricular pace eventVESVentricular extra-systoleVp, VPVentricular pace (stimulation) eventVs, VSVentricular sense eventVrsVentricular refractory sense eventVAny ventricular eventVFventricular fibrillationVTventricular tachycardiaVVDInterventricular delay intervalΔVVDOffset VVD